I've been playing with MythTV for quite some time now, and still havent got around to doing the final install eg putting the frontend in place etc. It's not the easiest thing in the world to get setup and working, but it is a pretty damn good piece of software.

My backend is a P4 3ghz with 1gb ram. It has 2x 200gb and 2x 160gb hard drives set up in a mix of software raids. It also has a PVR350 card for the recordings.
In hind sight I probably would go for the PVR250 instead as I'm not going to use the output of the 350.

I also have a frontend, P3 1ghz 512mb of ram and an NVidia card for TV out. This is what will eventually be put under the television in the lounge.
Both machines run SUSE, the frontend is 10 while the server is 9.3.

When I first started playing with Myth I tried both mandrake and fedora as there were packages available for both of these and an excellent howto for fedora, which is still mostly applicable for other distros. The howto is here: http://wilsonet.com/mythtv/However even though it was a pain to get myth compiled on SUSE (for me anyway) the advantages for me outweighed the disadvantages of the other distros (just my opinion, but I think SUSE rocks .